Thermal coagulation therapy may be used for the treatment of localized diseased tissue, e.g., tumors, in a diseased organ or body. Generally, a target volume of tissue is sufficiently heated to achieve a therapeutic effect, such as thermal coagulation. Tissue thermal coagulation depends on a number of factors, and temperatures in the range of 55-60.degree. C. are generally considered sufficient to provide enough energy to cause such coagulation. Cell death results from heating to these temperatures, and a region of irreversible thermal damage can be observed with imaging following the treatment. In addition, heating can be produced from minimally-invasive applicators, eliminating the need for open surgery, and potentially reducing recovery time and morbidity for patients. This approach has been used with some success in the treatment of isolated primary liver cancers and colorectal metastases for patients otherwise ineligible for surgery.
Interstitial thermal therapy is currently practiced by inserting heating applicators directly into a target site within an organ. Several energy sources have been integrated into interstitial heating applicators, including lasers, ultrasound, microwave, and radiofrequency energy. Preferably, interstitial thermal therapy delivers sufficient thermal energy to coagulate an entire target volume, while avoiding undesirable thermal damage to normal tissue. This strategy is referred to as “conformal thermal therapy.” One limitation of present interstitial thermal therapy technology is the inability to control or adjust the three-dimensional pattern of energy deposition dynamically during a treatment. Most current applicators act as point or line sources of energy resulting in highly symmetric patterns of energy deposition in tissue. This makes it difficult to treat targets with complex geometry accurately, and does not take full advantage of the imaging information available with imaging technology such as magnetic resonance imaging (MRI).
One application of interstitial heating is transurethral prostate thermal therapy, which selectively destroys diseased prostate tissue using a device located within the prostatic urethra, and preserves adjacent normal tissues such as the rectal and bladder walls. Disease targets include prostate cancer and benign prostatic hyperplasia (BPH). Current transurethral thermal therapy technologies are incapable of producing a thermal treatment (cell death) pattern that conforms to the geometry of the prostate gland.